1. Field of the invention
The present invention relates to a signal processing device for detecting weak signals and a radiation measurement device using the signal processing device.
2. Description of the Related Art
Recently, there has been studied a method of using Stochastic Resonance (SR) to detect weak signals buried in background noise. For example, there is known the method of adding noise to an input signal containing a weak signal thereby to cause stochastic resonance in the weak signal (for example, see Japanese Patent Application Publication No. 2013-135244, referred to as “ JP2013-135244A” below). In this method for causing stochastic resonance, a noise added signal is subjected to threshold processing and converted into a binary signal thereby to reproduce a weak signal.
However, a stochastic resonance circuit disclosed in JP2013-135244A is configured to add noise to an input signal containing a weak signal, and such a stochastic resonance circuit has a problem that, depending on an SN (Signal-Noise) ratio representing a ratio of a weak signal as a detection target to background noise, addition of noise may cause deterioration in the SN ratio of the weak signal. For example, assuming that a weak signal as a detection target has a much higher signal level than background noise, if the noise is added to an input signal to cause stochastic resonance, the SN ratio of the weak signal may be degraded to disable reproduction of the weak signal.